Any chance “The Hurt Locker” had of seriously challenging “Avatar” for Best Picture on Oscar night were vaporized when SAG’s ensemble prize — its rough equivalent of best picture, where “Avatar” wasn’t nominated — instead went to “Inglourious Basterds.” Without the actors behind critics’ darling “The Hurt Locker,” Quentin Tarantino’s World War II fantasy becomes James Cameron’s main competition. “Up in the Air,” which also lost in this category, also looks like an also-ran for Oscar night after being the default leader for most of the fall.